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<H1 id="MPI_Graph_create">MPI_Graph_create</H1>
Makes a new communicator to which topology information 
<H2>Synopsis</H2>
<PRE>
</PRE>
<PRE>
int MPI_Graph_create(MPI_Comm comm_old, int nnodes, const int indx[],
                     const int edges[], int reorder, MPI_Comm *comm_graph)
</PRE>

<P>
<H2>Input Parameters</H2>
<DL>
<DT><B>comm_old </B> <DD> input communicator (handle)

<DT><B>nnodes </B> <DD> number of nodes in graph (integer)

<DT><B>indx </B> <DD> array of integers describing node degrees (see below)

<DT><B>edges </B> <DD> array of integers describing graph edges (see below)

<DT><B>reorder </B> <DD> ranking may be reordered (true) or not (false)
</DL>
<P>
<H2>Output Parameters</H2>
<DL>
<DT><B>comm_graph </B> <DD> communicator with graph topology added (handle)
</DL>
<P>
<H2>Notes</H2>
Each process must provide a description of the entire graph, not just the
neighbors of the calling process.
<P>
<H2>Algorithm</H2>
We ignore the <tt>reorder</tt> info currently.
<P>
<H2>Thread and Interrupt Safety</H2>
<P>
This routine is thread-safe.  This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks.  However, the routine is not interrupt safe.  Typically,
this is due to the use of memory allocation routines such as <tt>malloc
</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
<P>
<H2>Notes for Fortran</H2>
All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
an additional argument <tt>ierr</tt> at the end of the argument list.  <tt>ierr
</tt>is an integer and has the same meaning as the return value of the routine
in C.  In Fortran, MPI routines are subroutines, and are invoked with the
<tt>call</tt> statement.
<P>
All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
</tt>in Fortran.
<P>
<H2>Errors</H2>
<P>
All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
C routines as the value of the function and Fortran routines in the last
argument.  Before the value is returned, the current MPI error handler is
called.  By default, this error handler aborts the MPI job.  The error handler
may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
RMA windows).  The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
its use is deprecated.  The predefined error handler
<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
Note that MPI does <em>not</em> guarantee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.
<P>
<DL>
<DT><B>MPI_SUCCESS </B> <DD> No error; MPI routine completed successfully.
</DL>
<DL>
<DT><B>MPI_ERR_ARG </B> <DD> Invalid argument.  Some argument is invalid and is not
identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
</DL>
<DL>
<DT><B>MPI_ERR_COMM </B> <DD> Invalid communicator.  A common error is to use a null
communicator in a call (not even allowed in <tt>MPI_Comm_rank</tt>).
</DL>
<DL>
<DT><B>MPI_ERR_OTHER </B> <DD> Other error; use <tt>MPI_Error_string</tt> to get more information
about this error code. 
</DL>
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